Definition of Certain

definite but not specified or identified; "set aside a certain sum each week"; "to a certain degree"; "certain breeds do not make good pets"; "certain members have not paid their dues"; "a certain popular teacher"; "a certain Mrs. Jones"

having or feeling no doubt or uncertainty; confident and assured; "felt certain of success"; "was sure (or certain) she had seen it"; "was very sure in his beliefs"; "sure of her friends"

established beyond doubt or question; definitely known; "what is certain is that every effect must have a cause"; "it is certain that they were on the bus"; "his fate is certain"; "the date for the invasion is certain"